What is a Worked Example of Swap Costs?

Direct answer

A worked example of swap costs is a fully specified numerical scenario that shows how an overnight financing charge (or credit) is calculated for a held forex position. The goal is transparency: you state every assumption (trade direction, holding time, rate inputs, lot size, and the sign convention for “cost” vs “credit”), then compute the total swap over the chosen number of rollovers.

In the example below, no real-time prices are used. It’s an educational calculation framework, not a prediction of future outcomes.

Mechanism or definition

A forex “swap cost” is the financing effect of rolling (carrying) a position from one trading day to the next. Conceptually, it reflects the difference between interest rates in the two currencies involved, applied according to the contract’s size and the broker/platform’s rollover rules.

To make a worked example verifiable, you separate stable mechanics from variable conditions:

• Stable mechanics (general idea): holding overnight triggers a rollover; the swap amount depends on direction and the interest-rate differential of the two currencies.
• Variable conditions: the exact numeric inputs (the effective rollover rates), the rollover time, the instrument contract specifications, and provider-specific sign conventions (when a swap is shown as negative/positive) can differ.

Key sign assumption you must state: in many interfaces, a “cost” may appear as a negative value to the account, while a “credit” may appear as positive. Because providers can present signs differently, your example should explicitly define how you interpret the numbers.

Evidence or example

Worked numerical scenario (with explicit assumptions)

Assume a trader places a forex trade and holds it overnight for 2 rollover events. Use the following assumptions so the math can be checked independently:

1. Instrument: a forex contract where the swap is reported per standard lot.
2. Position: you are long the base currency (direction stated explicitly).
3. Holding: the position is held across 2 overnight rollovers.
4. Swap rate inputs: the provider applies an effective swap amount (per standard lot) of −3.50 account currency units for each rollover event for this direction.
5. Lot size: 1.0 standard lot.
6. No other costs: ignore spreads, commissions, and any fees not included in swap.
7. Sign convention: “−” means the swap reduces account balance (a cost).

Now compute:

• Swap per rollover = (−3.50) × (1.0 lot) = −3.50
• Total swap over 2 rollovers = (−3.50) × 2 = −7.00

If you instead assumed the opposite direction (short position) and the effective swap per rollover for that direction were +2.00 per standard lot (a credit), then the same framework gives:

• Total swap = (+2.00) × 2 = +4.00 credit (under the same sign convention).

What this example teaches

The purpose is not the particular numbers; it’s the method:

• You fix direction and holding time.
• You use provider-style effective swap-per-rollover inputs.
• You multiply by lot size and number of rollovers.
• You keep the sign convention explicit so “cost vs credit” is unambiguous.

Limitations and risks

1. Provider-specific inputs: The effective swap values (and their signs) come from the broker/platform’s implementation. Even when the underlying concept is interest-rate differential, the displayed swap can differ.
2. Rollover timing: Swap is tied to rollover events, so the number of rollovers depends on the actual time the position is held across cutoffs.
3. Contract specifications: Lot size definitions and contract units differ across instruments and jurisdictions; a calculation based on “per lot” assumes consistent contract specs.
4. Market changes: While your example shows a static calculation, the real swap-rate inputs can change over time with interest-rate conditions.
5. Failure mode—misreading signs: A common verification error is treating a credit as a cost (or vice versa) because different platforms can display signs differently.

For the most accurate self-check, you should compare the worked framework against the swap fields you see on your platform for the same instrument and direction, then confirm how many rollover events occur during the holding window.

Verification or next question

To independently verify swap costs for any specific case, answer these questions before calculating:

• What direction is the position (long vs short)? - How many rollover events occur in your holding period (based on rollover time)? - What swap amount does the provider display per lot for that direction?